Can I take a drop in class 12th even if I have appeared for my practicals?

Yes you can. But I suggest you should give a chance to even get pass. If you appeared in practical than it does not matter if you will not give the board examination. The result is the sum of the practical and theory exam. Before wasting a year must take a look on your past of the year and how you can bet that it will not happen this year.
I am also a failed student in 11th but I reappear in the same class I got 81 percentage in my board exam I know this is not a good score but I break my silence in the life.